Realistically any summary will be missing some amount of detail so if you want to know exactly then you'll have to read the source. The source is pretty accessible though, you can actually just click the recipe names and they'll take you to the source on GitHub:
You can also check the metadata.rb of each recipe for a brief description.
At a high level:
- opsworks_initial_setup - Installs basic utilities and dependencies such as NTP, vim and sets basic config such as limits.conf
- ssh_* - OpsWorks supports managing SSH users via the OpsWorks interface, most of the SSH recipes are to support that functionality.
- mysql::client - Obviously installs the MySQL client, although this recipe actually does nothing if the stack doesn't involve MySQL
- opsworks_ganglia* - Does nothing unless you have a ganglia layer
- dependencies - Supports the OS packages functionality of OpsWorks and I think also installs some dependencies needed by the OpsWorks agent
- ebs - Supports the EBS functionality of OpsWorks
- agent_version - Updates the agent
In general, most of these recipes are supporting functionality built into OpsWorks but you could overwrite any of the recipes to remove anything you feel is detrimental.
To some extent the benefit of OpsWorks is to provide sensible defaults, so in most cases it's pragmatic to establish a need to alter the defaults before setting out to customise things.